1. Field of the Invention
This invention relates to swimming pool covers, and more particularly, to methods and apparatus for providing sufficient slack in the leading edge of swimming pool covers so that the cover material is not subjected to undue tension even when the leading edge is raised.
2. The Prior Art
For a number of reasons, it is advantageous and increasingly common to provide swimming pools with a swimming pool cover. For example, a cover substantially reduces pool maintenance time and costs by helping to keep dirt, leaves, and other debris from getting into the pool. A swimming pool cover also decreases the need for chemical treatment, and it can further help to minimize the energy which is required to heat the pool. Additionally, the use of a swimming pool cover when the pool is not in use greatly reduces the risk that an unattended child will accidentally enter the pool and be drowned.
Of course, one way to cover a swimming pool is to manually extend a large cover sheet across the pool and to thereafter secure the edges of the cover sheet to the pool deck. However, such a procedure is usually quite time consuming, and, additionally, more than one individual may be required in order to cover the pool properly. Therefore, in order to increase the convenience of using a pool cover, and in order to make the frequent use of a pool cover more practicable, many swimming pool owners make use of a pool cover which is mechanically extended and retracted across the swimming pool by an electric motor.
One type of pool cover which is well adapted to such mechanical extension and retraction comprises a large, rectangular cover sheet having thickened, or beaded, side edges. The beaded edges of the cover sheet are slidably received in open channels formed in respective, parallel tracks which are positioned adjacent to opposite sides of the swimming pool. Typically, there is sufficient slack in the cover sheet such that a portion of the cover sheet rests on the surface of the water after it is fully extended across the pool, with the beaded side edges being continuously maintained in and laterally secured by the respective channels.
When the swimming pool cover is not in use, the cover sheet is rolled upon an elongated cylindrical member which is located at one end of the pool. In order to cover the pool, the electric motor draws the edges of the cover sheet along the respective tracks so as to extend the cover sheet from one end of the swimming pool to the other. When the pool is to be uncovered, the motor rolls the cover sheet back onto the cylindrical member, and the cover sheet is thus retracted and stored for future use.
In order to minimize the likelihood that the leading edge of the pool cover will dip into the water during extension, thereby causing the water to flow onto the top of the cover sheet, mechanically extendible swimming pool covers are usually provided with a rigid leading edge. Optionally, the cover sheet may also have a central gore or a screen formed therein adjacent the leading edge of the pool cover, in order to allow for the drainage of any water which might collect on the cover sheet.
When a pool cover of the type described above is installed on a substantially rectangular swimming pool at the same time as such pool is being constructed, the side tracks are generally mounted inside the pool just below the pool deck. Thus, when the beaded edges of the cover sheet are properly positioned in their respective channels, the cover extends across the pool from one inside edge to the other. In such a configuration, the pool cover may be used without modification, and it can also be mechanically extended and retracted without difficulty.
The situation is quite different, however, when a mechanically extendible pool cover is installed on an existing rectangular swimming pool or on any pool which has a non-rectangular shape. In such cases, it is generally preferable to install a rectangular pool cover outside of the pool such that the parallel side tracks are secured to the top of the pool deck adjacent to the pool edges. This type of installation both eliminates the need to remove a portion of the pool deck and pool sides on existing pools and avoids the operational difficulties caused by attempting to mechanically extend and retract an odd-shaped swimming pool cover.
However, several difficulties arise when the pool cover is installed outside of the pool in this manner. First, it will be appreciated that a portion of the pool deck will necessarily underlie the pool cover after the cover is fully extended over the swimming pool, particularly in the case of odd-shaped pools. As a result, the pool cover will tend to drag across the pool deck's surface as it is extended and retracted, thereby making cover extension and retraction somewhat more difficult. Additionally, the pool cover's rigid leading edge may similarly drag across the surface of the deck, thereby causing undue wear both to the pool deck and to the rigid leading edge. Further, the rigid leading edge, which generally tends to sag slightly in the middle, may sometimes be unable to clear the odd-shaped or the endmost portions of the pool deck.
It has been found that the above difficulties may be overcome if the pool cover's leading edge is raised above the parallel side tracks. By so raising the leading edge, one can significantly reduce the frictional forces which resist pool cover extension and retraction. Further, raising the pool cover's leading edge eliminates the possibility that the leading edge will drag across the pool deck, and it thus insures that the leading edge will entirely clear all portions of the deck.
The exact height to which the leading edge must be raised is determined by the characteristics of the particular swimming pool. For example, when a swimming pool is substantially rectangular, the side tracks may be secured quite close to the pool edges, which are usually at about the same height. Therefore, when a pool cover is installed on an existing rectangular pool, it is typically necessary to raise the leading edge of the pool cover only slightly in order to achieve the desired benefits.
This is not the case, however, when such a cover is installed on an odd-shaped pool. Since the swimming pool cover sheet is rectangular, the side tracks must necessarily be laid down in substantially parallel, straight lines, regardless of the shape of the pool. Thus, when an odd-shaped pool is covered, some sections of the tracks may be positioned several feet away from the pool, while other track sections would be very close to the pool edge.
Since the pool deck typically slopes away from the pool in order to provide for proper drainage (this slope is generally about one inch for every four feet of lateral distance from the pool), the distant sections of the tracks may be several inches lower than the portions of the pool deck which are near the edges of the swimming pool. Consequently, in order to insure proper pool cover operation on odd-shaped pools, it is sometimes necessary to raise the pool cover's leading edge six or more inches above the two side tracks. Unfortunately, when attempting to appropriately raise a pool cover's leading edge so as to overcome the difficulties set forth above, several additional difficulties are encountered.
First, since the beaded side edges of the cover sheet are held captive in channels formed in the respective tracks, it may sometimes be impossible to raise the leading edge an amount sufficient to achieve the desired benefits. Additionally, any significant raising of the leading edge of the pool cover increases the tension in the cover sheet and, more particularly, in the beaded side edges of the cover sheet. This tension is often further increased after pool cover installation due to shrinking of the cover material.
Tension in the cover sheet may be detrimental to pool cover performance in a number of ways. For example, when placed under tension, the cover sheet may stretch or tear at a location adjacent the leading edge or the beaded side edges of the cover sheet may disengage from their respective channels. Further, excessive cover sheet tension may hinder the proper extension and retraction of the pool cover, or it may also cause the pool cover to be extended and retracted unevenly.
One solution to these additional problems was described in U.S. Pat. No. 4,001,900. Therein, it is suggested that triangular gores may be sewn onto each side of the cover sheet adjacent the leading edge so as to provide sufficient slack in the cover sheet to allow the leading edge to be raised to the proper height without creating undue tension. Although the addition of such side gores to the cover sheet has proven helpful, it has not proven to be completely satisfactory in several respects.
It will be appreciated that it is difficult to determine the exact height to which the pool cover's leading edge must be raised prior to the time that the pool cover is actually being installed. For this reason, it is also difficult to tell how large to make the side gores of the cover sheet prior to the time of pool cover installation. Since it is both time consuming and expensive to custom cut and fit the side gores at the installation site, it has become common for installers to prepare and have on hand several standard sizes of side gores. Thus, while the pool cover is being installed, two of the standard gores which are closest to the actual size needed are sewn onto the cover sheet by hand.
Since such gores are pre-cut to standard sizes, it is understandable that, in most cases, the side gores which are installed will be slightly larger than is actually necessary for the particular pool. If the side gores of the pool cover are too large, the gore material tends to bunch and to rub against the pool sides and deck when the pool cover is being extended and retracted. This rubbing significantly increases the noise during pool cover extension and retraction. Further, after a relatively short time, the gore material tends to wear so as to necessitate its replacement.
Of course, one potential way of eliminating the difficulties caused by oversized side gores is to raise the leading edge of the pool cover the additional amount which is needed in order to take up the excess slack in the gore material. However, when a pool cover's leading edge is raised more than the amount which is necessary to insure that the leading edge clears the pool deck, dirt tends to get into the pool under the leading edge, thereby nullifying some of the benefits of a swimming pool cover.
Additionally, if the leading edge is raised more than necessary, the appearance of the pool cover is generally less desirable, the pool cover is somewhat more of an obstruction, and a larger amount of gore material is exposed to the possibility of damage. Since these considerations are typically quite important to swimming pool owners, most owners prefer either to tolerate oversized side gores or to incur the additional expense of having their cover's side gores custom cut and fitted.
In addition, the prior art method of attaching side gores to a swimming pool cover has also been found to be somewhat undesirable. Since, as mentioned above, the exact gore size which is needed is unknown until pool cover installation begins, the necessary side gores are typically sewn onto the pool cover sheet by hand at the installation site. This sewing and fitting process can often be quite time consuming and tedious. Consequently, the sewing and fitting of side gores at the installation site may significantly increase the cost of producing and installing a swimming pool cover.
Accordingly, it would be an improvement in the art to provide a standard swimming pool cover with a raised leading edge, wherein the cover sheet is not subjected to undue tension, and which may be properly installed on various types of swimming pools without the need for custom cutting and fitting the appropriate size of side gores adjacent the leading edge of the pool cover. It would also be an improvement in the art to provide a mechanically extendible swimming pool cover which can be economically installed without using oversized side gores and without raising the leading edge of the pool cover more than the amount which is necessary to enable the cover's leading edge to clear the pool deck. Further, it would be an improvement in the art to provide a means whereby the requirement of sewing side gores onto the cover sheet at the installation site is avoided, even though the exact height to which the leading edge of the pool cover will need to be raised is unknown before installation begins. Still further, it would be an improvement in the art to provide a method for installing mechanically extendible swimming pool covers which eliminates the need for separately sewing on side gores but which also avoids any undue tension in the pool cover material caused by raising the leading edge of the pool cover. Such apparatus and methods are disclosed and claimed herein.